An internal quality assessment scheme (IQAS) can be used to monitor the quality of work more frequently and reproduce normal test conditions more accurately that NEQAS. IQAS samples can be provided in sufficient numbers and should not be more vigorously tested that any other routine specimen.In the IQAS some specimens received in the laboratory are resubmitted for testing anonymously, thus all activities involved in the passage of specimens through the laboratory starting from reception and ending in the dispatch of final report can be monitored.8 The samples chosen can realistically reflect the diversity of tests in current use, and the numbers can be sufficiently high to monitor all laboratory procedures with precision but without increasing the workload excessively.Here, we report on the organisation and performance ofan IQAS used in the diagnostic virology laboratory of the Clinical Microbiology and Public Heath Laboratory, Cambridge, since April 1991 to assess the performance of the serology section. For organisational reasons, antibodies against other microbiological agents (Chlamydia sp, Coxiella burnetii, Mycoplasma pneumoniae, Legionella pneumophilia, Toxoplasma gondii) were also tested in this section. A total of 715 anonymous serum samples (IQAS) to test 3245 individual procedures